/**
*      author: Y_Yao
*      created: 2024-12-07 19:52:06
**/

#include<bits/stdc++.h>

#define int LL
using namespace std;
using LL = long long;
const LL LLINF = 1e18;
const int INF = 0x3f3f3f3f;
const int N = 100 + 7;
int T[N],V[N];
int n;

void solve()
{
    cin >> n;
    int sum = 0;
    for(int i = 1;i <= n;i++)
    {
        cin >> T[i] >> V[i];
        if(i > 1)
        sum -= T[i] - T[i-1];
        if(sum < 0) sum = 0;

        sum += V[i];
        //cout << sum << " ";
    }

    cout << sum << endl;

}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    int t = 1;
    //cin >> t;
    while(t--)
    {
        solve();
    }
    return 0;
}